The present invention relates to an eyeglass lens grinding apparatus for grinding the periphery of an eyeglass lens.
An apparatus is known, in which a subject lens is clamped by two lens rotating shafts, the lens is rotated by synchronously rotating these two lens rotating shafts by mechanically linking them by means of pulleys, gears, and timing belts, and the lens is ground by moving the lens rotating shafts relative to an abrasive wheel.
In processing, a mounting jig such as a suction cup secured to the front surface side of the lens is fitted to a cup holder provided on one lens rotating shaft, the other lens rotating shaft having a lens holder is moved toward the cup holder to press and clamp the lens. An angle of rotation of the lens during grinding is controlled using a pulse motor which rotates the lens rotating shafts synchronously.
If the force (chuck pressure) with which the lens is pressed by the two lens rotating shafts is weak, the so-called axial offset occurs in which an actual axial angle of the lens is not coincident with an intended angle of rotation of the lens.
Major factors causing this axial offset are a processing error that occurs due to the deformation of a rubber portion of the mounting jig caused by the processing resistance applied by the abrasive wheel during lens grinding, and an error that occurs in the controlled angle of the axis of rotation of the lens due to an insufficient rigidity of a lens rotating mechanism section. The axial offset deteriorates the accuracy of the axial angle of the lens and hinders the accurate reproducibility of the finished shape.
The reduction of the axial offset depends solely on the reduction of the deformation amount of the rubber portion by increasing the chuck pressure to apply a strong pressure to the rubber portion of the mounting jig. However, if an excessively large chuck pressure is applied, the coating film or layer on the lens surface is damaged or broken and, in the case of a glass lens, the lens itself is broken.